Delivery of enzyme across the blood-brain barrier to correct neuronal storage represents a major unmet need since nearly 90% of lysosomal storage diseases involve the central nervous system and conventional enzyme replacement therapy does not correct storage in the brain. The broad goal of this research is to continue studies of newly discovered routes of transport of lysosomal enzymes to brain and their relevance to correcting neuronal storage by enzyme replacement therapy. We will use 2- glucuronidase and 1-iduronidase as model enzymes and murine mucopolysaccharidosis type VII (MPS VII; Sly disease) and MPS I (Hurler disease) as model lysosomal storage diseases. We seek to capitalize on recent breakthroughs addressing correction of neuronal storage, including: 1) The discovery that mannose 6-phosphate (M6P) mediated transcytosis (endocytosis at the luminal membrane followed rapidly by exocytosis at the abluminal membrane without going through the lysosome) can be upregulated pharmacologically in adult mouse brain to allow transport of enzyme across the blood-brain barrier comparable to that seen in the neonate; 2) The discovery of a novel route for chemically modified enzyme to correct neuronal storage when maintained at a high circulating level in plasma over a sustained period; and, 3) The findings that resistant sites not accessible to native enzyme can be targeted successfully using chimeric enzymes that target other cell surface receptors. We have four Specific Aims: 1) Determine the mechanism and significance of pharmacological upregulation of M6P receptor mediated transcytosis of lysosomal enzymes across the blood-brain barrier. 2) Determine the mechanism, efficacy, and generality of neuronal correction by periodate (PerT) modified enzyme. 3) Determine the efficacy of transferrin-iduronidase and transferrin-2-glucuronidase chimeric enzymes in crossing the BBB and correcting neuronal storage in murine MPS I and MPS VII mouse models. We will use a variety of biochemical, cell biological, immunological, and molecular genetic approaches and take advantage of novel mouse models of MPS VII produced in our laboratory by transgenic and mouse knockout technologies. We combine histochemistry, histopathology, and immunoelectron microscopy to measure enzyme delivery to brain and other resistant sites of storage. The answers sought have fundamental significance and should provide information leading to novel therapeutic approaches to enzyme replacement for lysosomal and other storage diseases involving the central nervous system.